Conventionally, the surface temperature distribution during operation of a semiconductor device, especially a high power semiconductor device is measured by a scanning type radiation thermometer. For example, during an accelerated temperature test, an infrared ray scanning type surface thermometer (thermoviewer) which measures the quantity of infrared ray emitted from the surface by scanning the same is used for measuring the temperature distribution at the surface of the semiconductor device. An example of a thermoviewer is the "Computerm" produced by Barnes Engineering Division of EDO Corporation, 88 Long Hill Cross Roads, P.O. Box 867, Shelton, CT, 06484, U.S.A.. The construction of this device is shown in FIG. 6. The method of measuring temperature distribution with this apparatus is described below.
First of all, the surface of a sample semiconductor device 200 on an electronic heating/cooling stage 100 is divided into a plurality of two dimensional areas along X-Y coordinates. A scanning head 300 reads data for the respective areas of the partitioned surface. Furthermore, a memory 410 having addresses corresponding to the respective areas of the partitioned surfaces is prepared in the computer 400. This memory 410 includes an emissivity data memory, an emission data memory, and a calculated temperature data memory.
At the establishment of the initial data, emissivity is calculated based on the emission from the sample 200 at two different temperatures (such as 40.degree. C. and 60.degree. C.,) and obtained data are stored in the emissivity data memory. The emission from the sample 200 which is heated up to an established temperature for the acceleration test is measured and the obtained data is stored in the emission quantity data memory. After the establishment of the initial data, the sample 200 heated up to the established temperature of the accelerated test and operated. The emission from the sample 200 in that state is measured and its data is stored at the emission data memory. The computer 400 calculates the temperature for each of the respective partitioned areas of the surface of the sample 200 on the basis of the data stored at the emissivity data memory and emission data memory, and obtained data are stored in the calculated temperature data memory. The temperature distribution is displayed or output on a color monitor 600 or a printer 500 on the basis of the stored data. A cursor 610 is displayed on the screen of the color monitor 600. The instructions for instructing the above described processing are input from the keyboard 700.
As disclosed in the manual "OPERATOR'S MANUAL FOR COMPUTERM" of the above described "Computerm", the initial data are established for each time the sample 200 is fixed on the stage 100 during measurement of the sample 200. Furthermore, the initial data are established each time the sample 200 is moved during the measurement. This is because when the fixed position of the sample 200 is shifted, the addresses of the partitioned surface areas are shifted.
Therefore, in a case where the measurement is repeated at the same established temperature accelerated test, it is necessary to measure the initial data each time a new sample 200 is mounted.
In the prior art semiconductor device of such construction, when the temperature distribution of the surface is to be measured, the initial data has to be established each time a new sample 200 is mounted on the stage 100. Furthermore, even when the sample 200 is shifted from the initial position during a measurement, the initial data has to be again established. This has resulted in a lengthy measurement time.